Powder injection molding is a well known technique for manufacturing articles from particulate material and examples of such systems are represented in: U.S. Pat. No. 5,415,830, Zhang et al., U.S. Pat. No. 5,397,531, Peiris et al., U.S. Pat. No. 5,332,537, Hens et at., U.S. Pat. No. 5,155,158, Kim et al., U.S. Pat. No. 5,059,388, Kihara et at., U.S. Pat. No. 4,765,950, Johnson, U.S. Pat. No. 4,661,315, Wiech, U.S. Pat. No. 4,415,528, Wiech, U.S. Pat. No. 4,225,345, Adee et at., and U.S. Pat. No. 4,197,118, Wiech. In these prior art systems, powders and binders are mixed to form the feedstock which is powder injection molded. The feedstock production is the most important step in the powder injection molding technology. If components are manufactured from inferior feedstock, it will be difficult, if not impossible to produce consistent components of high tolerances without secondary processes such as coining or machining.
Feedstock homogeneity and compositional accuracy are a major challenge for manufacturers using powder injection molding. Problems with components such as cracking and nonuniform shrinkage during debinding and sintering can often be traced back to feedstock production.
Conventional practice in powder injection molding is that powders having the elemental composition of the desired final product are mixed with an additive and a binder mixture to form the feedstock. The binder mixture may contain two primary components in a heterogeneous mixture. The first component of the binder, also referred to as the major component, is typically a polymer component such as a wax or a water soluble component. This is used, in part, to provide a medium to transport the powder into the mold. The major component is typically designed for good moldability and easy removal during the debinding phase. The second component of the binder, also referred to as the backbone component, is used to retain the shape of the compact while the first component is removed. The backbone component is, generally, removed just before the powder particles start to sinter.
These known feedstocks have solids loadings around 50 to 60 percent by volume. Such systems have inherent problems in that a relatively large proportion of the feedstock is binder which is used to make the feedstock flow, causing significant shrinkage of the molded components during the debinding and sintering phases. Moreover, during the thermal removal of the binder, the components are heated through the molding temperature of the feedstock, causing shape loss. Shape loss also occurs in these prior art systems because the binder components with a lower molecular weight decompose or volatilize during the mixing of the feedstock and during injection molding. As a result of this shrinkage and deformation, parts manufactured by these known methods may require expensive supporting equipment to retain the shape of the molded component prior to sintering. Additionally, the parts may require machining after sintering if tolerances are not met. The parts are also limited to relatively small component sizes.